The invention relates to a cell for measuring the activity of a liquid.
Spectrophotometric cells are routinely used to measure concentrations of uranium and plutonium for example in radioactive liquids. They comprise one end called an optode which is immersed in the liquid containing radioactive elements, a spectrophotometer which is placed in a zone accessible to operators and which measures the concentrations of the elements and displays results, and an optic fibre which connects the spectrophotometer to the optode.
An optode is generally made of a quartz cylinder through which pass two parallel branches of the optic fibre allocated to out and return travel of the light by means of a reflection produced in the bottom part of the optode. A slit is cut in the quartz cylinder to interrupt the fibre over part of its length belonging to the return branch or both branches; this length is called the xe2x80x9coptic distancexe2x80x9d and serves to collect the photons emitted by the active particles in the liquid for measurement purposes. It is therefore essential that the optic distance must be fully immersed in the liquid to be measured.
At the present time, measurements consist of immersing the optode in a beaker containing a sample of liquid to be analysed, which requires certain manipulations. Other manipulations are required before each new use, since the optode must be rinsed then calibrated. The use of these spectrophotometric devices is therefore slow and tiresome, and requires precautionary measures to avoid contamination.
The measuring cell put forward here, which shall be described in detail below, offers the chief advantages of allowing direct, fast and safe measuring of a liquid without having to draw off a liquid sample from the circuit in which it is contained to pour it into a container, nor does it require complicated manipulations. Above all, it can allow easy rinsing and calibrating even though it is normally not accessible.
The concrete measures taken to achieve these advantages consisted of integrating the optode at the end of a probe, and of causing a portion of a flow circuit of the liquid to be measured to pass through the cell such that the optode is immersed in this portion of circuit. A rinsing circuit is added which leads to the optode so that it can be rinsed at will. The optode remains inserted in the cell but may be oriented either towards the liquid to be measured or towards the rinsing liquid.
To resume, the invention in its more general form concerns a cell for measuring the activity of a liquid, comprising a probe, the probe being equipped with a cylindrical measuring end, characterised in that it comprises a liquid flow-pipe provided with a cylindrical alveolus in which the cylindrical end is inserted, the alveolus opening on one side into the flow-pipe and being delimited on the other side by a wall, a clearance existing between the end of the probe and the wall; in addition, a rinsing liquid duct leads into the alveolus via the wall, and the probe is mounted so that it can pivot freely within the cell.
Immersion of the optode is guaranteed if an overflow barrier is placed downstream from the alveolus across the rinsing liquid duct.